The present invention comprises an improvement of the above-identified copending patent application.
Said copending application relates to a water based ink jet printing ink capable of producing high quality, high density images on a wide variety of substrates, while maintaining good archival properties.
Its formulation of water soluble dye, ammonia soluble acrylic binder, plasticizer, humectant, surfactant, biocide, chelating agent, and ammonium hydroxide produces an ink jet ink solution that is capable of being printed on a variety of substrates, both absorptive and nonabsorptive. This ink sets up in its own matrix, above the substrate, and is water-fast and wet smear resistant upon setting. At the same time, this ink produces high quality, high density images.
This copending application is based upon the discovery that acrylic binders that are soluble in a base, such as ammonium hydroxide, and insoluble in water, when formulated with compatible dyes and fugitive amines, yield waterfast images on a variety of nonabsorptive and absorptive substrates.
The invention requires a binder that is a copolymer of acrylic acid. The carboxylic acid group is an active group capable of being solubilized in the ink by a fugitive amine such as ammonia. The other binder constituent is a compound of a group such as styrene which helps insolubilize the copolymer of acrylic acid once the ink is printed and some of the amines are driven off. The resulting copolymer of styrene and acrylic acid is of a molecular weight about 10,000, and the styrene to acrylic acid proportion by weight is about 2 to 1. One such binder is Joncryl 67, a styrenated acrylic from S. C. Johnson Co. In general, the binder is used in amounts 3 to 15% by weight and preferably 8 to 11% by weight of the ink's composition.
A dye is used in that invention which is compatible with the binder. That is, the dye and binder, in certain ratios, are capable of forming waterfast, smear resistant images. Certain acid, basic, direct, solvent and polymer dyes are effective. The enhanced archival properties of the ink of that invention are thought to be a result of one or more of the following: entrapment of the dye in the insolubilized polymer film; dye-to-polymer noncomplexed form of attraction; and/or the dye is complexed to the polymer. Examples of compatible dyes are Direct Black 19 (examples III and IV), Acid Black 2, Solvent Red 124 (example I), Basic Red 12 (example II) and Acid Blue 90. The amount of colorant used is dependent on its purity and dye strength, and is limited by its solubility. In general, the dye or mixture of dyes is used in amounts 1/2 to 8% by weight.
In addition to dye and binder, the ink of that invention contains several selected materials necessary for a jet ink. The binder requires a plasticizer in order to obtain good print. Also, the ink must contain an anti-crusting agent so the ink will not have unreasonable start-up problems or stream misdirection. A polyethylene glycol such as Union Carbide Carbowax 200 brand serves both as a plasticizer and anti-crusting agent and can be used in the proportion 3 to 12% by weight, preferably 4 to 10% by weight. Carbowax is a water soluble lubricant, a known solvent for dyes, resins and proteins, and a known plasticizer for special printing inks.
As stated in that application, a surfactant can be used to adjust the surface tension so that smooth print is obtainable on a wide variety of substrates. The surface tension is adjusted to between about 30 to 40 dynes/cm. Triton GR5M, a water soluble surfactant from Rohm & Haas Co. which is dioctyl sodium sulfosuccinate, is one example of an acceptable surfactant.
Also, as stated therein, appropriate fungicide or anti-bacterial agent(s) may be used, and in general the type and amount will be dependent on the impurities in the ink and the dye solubility. Sodium omadine, a derivative of pyridinethione (sodium-2-pyridinethiol 1-oxide) having bactericide-fungicide properties is preferred, as is the organic chelating agent EDTA acid. NM2P (N-methyl-2-pyrrolidone) is used as a solubilizing agent.